When in flower, a snowball viburnum is loaded with white rounded masses of flowers, so much as to mask the branches and any leaves. At first glance, you may think it's a rare form of hydrangea. Two species of viburnum shrubs are known as snowball bushes: Chinese snowball (Viburnum macrocephalum) and the Japanese snowball (V. plicatum f. plicatum). Never transplant a viburnum while it's in flower or in the process of pushing out new leaves. Wait until fall as the plant is going dormant.
Viburnum shrubs tend to develop a fibrous, somewhat shallow root system. This can make transplanting snowball viburnum shrubs a bit easier, provided enough of the root system is retained during the transplant process. Dig out as large of a root ball as possible, taking care to minimise damage to the roots within the soil mass. Ideally, cutting into the soil with a spade at least 12 inches from the shrub's branch base maintains some soil and root matrix in the root ball. Larger root balls are better, but can become too heavy to move and handle during transplanting.
The best time to dig up and transplant a snowball viburnum is in fall. The precise timing in fall depends on latitude or elevation. When the shrub's leaves are turning colours and dropping off until it's fully barren, it's time to transplant. Fall planting takes advantage of the cooler temperatures and often moist soil conditions. Until the soil freezes, roots can grow after fall transplanting and begin to establish. The second best time to transplant is in spring, but plants tend to display increased stress and stunted growth afterward.
The two types of snowball viburnums survive winters across U.S. Department of Agriculture plant hardiness zones 5b through 9a. Winters are colder in zones 5b and 6, so fall transplanting may need to occur as early as September to allow ample time for some root regrowth before the ground freezes. In the coldest, windiest parts of zones 5b, early spring transplanting may be best. Zone 5 winters may be too cold for a stressed, newly transplanted shrub to survive. In zones 7 and 8, fall planting is best and can be delayed until late October or into November.
Snowball viburnum shrubs sustain significant shock after having root systems cut and diminished during transplanting. It's imperative that the root ball is planted at the same depth it previously was in the new planting hole. Thoroughly water after planting to moisten roots and bring soil particles in contact with remaining roots, eliminating air pockets. Keep the soil evenly moist for the first six months after transplanting; water as long as the soil is not frozen.